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Apple publishes instructions on moving your entire music collection from one computer to another using an iPod in disk mode. The two catches are that your entire library has to fit on whatever size iPod you have, and that you have to go PC to PC or Mac to Mac (no cross-pollination).

This would totally work with your documents and other data and applications as well. See more on workin' the iPod disk mode in previous Lifehacker feature, The self-sustaining iPod.